TRT lens.. set me straight!

[darinwc]

"1.88 + 1.57 = 3.45 diopters

1/3.45 = 0.290 meters = 11.4""

Barry, I think the spacing adds some complexity to the math but I think its mostly right.

[Barry S]

Yeah, I know that these kind of calculations apply to simple thin lenses, but if you apply it to the existing TRTC lenses, they work out exactly as labeled. So I figure it's got to be pretty close.

[df cardwell]

Random stuff

• Gundlach designed the lens to step around the B&L license from Zeiss,
splitting the 4th cell into a 5th. When the lens is assembled properly, it will perform like a Protar.
Few TRs, however, are correctly centered, which might limit you to a 3x or 4x enlargement !

• Each component of a Protar (or TR) is the equivalent as a Rapid Rectilinear lens, high quality image of a narrow field, at f/12.5.

• You MUST use a single convertible cell BEHIND the aperture.

• Using two cells, it seldom matters which cell is in the front or in the rear. Try it, see which performs best for you.

• With two cells, you should have a fully color corrected lens.

• With a single cell, you may want to use a strong yellow or orange filter for highest definition. If you are not obsessed by counting pine needles on a tree a mile away, you can probably get along without it.

• With the 21 & 25, you might not quite cover 8x10 wide open. Stopped down, 11x14 with a little movement. Test drive it, check the corners of the groundglass. If it corner detail is important, stop down until you can see a full, round diaphragm.

• With a single cell, each cell covers 8x10 and then some, but mind the corners: if detail is important, look through the cut corners of the GG !

•••••• HAVE FUN ! Expect fine results, not something quaint and blurzy. They were high quality optics a hundred years ago, and they can be today.

[Jim Fitzgerald]

Random stuff

• Gundlach designed the lens to step around the B&L license from Zeiss,
splitting the 4th cell into a 5th. When the lens is assembled properly, it will perform like a Protar.
Few TRs, however, are correctly centered, which might limit you to a 3x or 4x enlargement !

• Each component of a Protar (or TR) is the equivalent as a Rapid Rectilinear lens, high quality image of a narrow field, at f/12.5.

• You MUST use a single convertible cell BEHIND the aperture.

• Using two cells, it seldom matters which cell is in the front or in the rear. Try it, see which performs best for you.

• With two cells, you should have a fully color corrected lens.

• With a single cell, you may want to use a strong yellow or orange filter for highest definition. If you are not obsessed by counting pine needles on a tree a mile away, you can probably get along without it.

• With the 21 & 25, you might not quite cover 8x10 wide open. Stopped down, 11x14 with a little movement. Test drive it, check the corners of the groundglass. If it corner detail is important, stop down until you can see a full, round diaphragm.

• With a single cell, each cell covers 8x10 and then some, but mind the corners: if detail is important, look through the cut corners of the GG !

•••••• HAVE FUN ! Expect fine results, not something quaint and blurzy. They were high quality optics a hundred years ago, and they can be today.

Thanks for all of the very useful information. I'll certainly play with the different components and see what I get. If I can use this lens on 8x10 and 11x14 it would be great. I'm only contact printing so ultimate sharpness is not an issue. I am aware of the filter needed on the single component. Thanks for the reminder on using it on the rear only. I usually stop this lens down to 32-45 at least.

Jim

[Ole]

...
• You MUST use a single convertible cell BEHIND the aperture.

• Using two cells, it seldom matters which cell is in the front or in the rear. Try it, see which performs best for you.
...

I would replace MUST with SHOULD in the above - as long as you have enough bellows, use a single cell behind. If you run out of bellows before you get to focus, put it in front.

Also, and for the same reason, the shorter focal length should be behind the shutter when using two cells. Since the difference in needed extension in this case is minimal, that could even be said to be a must - unless you're shooting macro.